Capacitive squeeze protecting device

ABSTRACT

A capacitive squeeze protecting device having a high degree of security and flexibility for automatic doors. The squeeze protecting device is arranged to detect the presence of an object in a protection field comprising a housing and an antenna unit connected to a detecting circuit, which circuit is arranged to, via said antenna unit, detect capacitive variations in an electric or electromagnetic field at said antenna unit. The detecting circuit comprises means connected to said antenna unit arranged to detect a variation of the pressure at said antenna unit caused by a compressive force applied at said housing, wherein the presence of conductive as well as non-conductive object can be detected. Furthermore, the invention includes a system and methods for detecting for detecting the presence of an object in a protection field at a door.

This application claims the benefit of International Application NumberPCT/SE2003/001421, which was published in English on Mar. 25, 2004.

TECHNICAL FIELD

The present invention relates to a capacitive squeeze protecting devicewith a high security level and flexibility for use in automatic doors.

STATE OF THE ART

Automatically controlled doors and are used in a variety of locations,such as entrances, indoor passages, busses/underground trains/trains,garages, industrial plants, warehouses and elevators. Other applicationslying near at hand is different types of lifts and shutters or hatchersand furniture's, for example, mechanically driven beds and armchairs. Inthe context of this application all of these will henceforth be denotedas doors.

There exist a number of different types of automatic doors, for example,doors describing a circular movement (a movement of 360 degrees) androtating doors and traditional doors that often describes a movement of90 or 180 degrees. There is also doors moving linearly, for example,sliding doors and folding doors. Other doors move in principle around anshaft, for example, balance doors. Yet another type of door combinesdifferent types of movement patterns, for example, the linear movementand a final circular or vertical movement. A large group is roof mountedsliding doors and fast roller doors, which often have a significantimpact of the power consumption due to its size.

A higher opening speed/closing speed is highly desirable in, above all,an energy-saving point of view. However, this come into conflict withthe requirements of a increased stopping distance and security. It isdifficult to increase the speed using conventional contact rails withoutsidestepping statutory requirements regarding compressive force.

In this connection it should be noted that at a speed of 1 m/s of thedoor and a reaction time of the electronics of 100 ms from that thecontact rail emits a signal, the stopping distance will be approximately10 cm. Accordingly, if the speed is doubled, i.e. 2 m/s, the reactiontime will be approximately 20 cm.

Automatically controlled doors can cause personal injuries of differentkinds, for example, the door blades of rotating doors can, which due toreasons of comfort have a certain rotational speed which, in turn, giverise to a certain stopping distance and a significant kinetic energy,push passing people over before the door has stopped with attendantfalling injuries. One critical area is the distance between the movingdoor blade and the stationary stand or door post. If an object ispresent in that area and the contact rails of the door responds todirect mechanical contact, the door blade will collide with a personbefore it stops and, possibly, reverses.

In many cases sliding doors of busses and underground trains pushedpeople over, which in certain cases have resulted in that the person hasbeen ran over.

In order to prevent such accidents from occurring sensors are used tosense or detect whether a person is too close to the doors when they areclosing and thereby run the risk of being squeezed and/or pushed over.There are number of different types of sensors used for this purpose,for example, electric/mechanical contact rails, pneumatic/hydrauliccontact rails, volume sensors, line light sensors and capacitivesensors.

The most commonly used sensor principle for contact rails in automaticdoors is open electric circuits, which often is in-built in soft plasticor rubber. An open electric circuit be composed of two contact sheets ofmetal or conductive rubber arranged in parallel. When a pressure isapplied on the rail, the two contact sheets will contact each other andthe circuit is closed. For example, in U.S. Pat. Nos. 5,964,058 and5,438,798 examples of such devices are shown. In U.S. Pat. No. 5,027,552a system with electric conductors for contacting in combination with acapacitive conductor for range-finding is disclosed. One problem withthe device disclosed in U.S. Pat. No. 5,027,552 is that the capacitiveconductor is influenced by the electric conductors and of adjacentground planes in the door. Another problem is that it may arisecondensation in the space within the housing where the conductors arearranged, which may cause, for example, corrosion. A common problem withcontact sheets or with electric conductors of the above mentioned typeis that the direction of the compressive force must have a predeterminedangle of, for example, 90 degrees, in order to press the contact sheetstogether. Furthermore, the contact sheets will be deformed by powerfuldamage as they usually are made of metal, which may give rise tofunctional problem. Finally, there is a risk that gravel, dust, rubberparts or other non-conducting particles may land between the contactssheets and thereby prevent contact between them.

Another common sensor principle is closed electric circuits. A closedelectric circuit may consist of a conductor, which, in turn, consists ofa number of smaller conductors kept together by a resilient device. Whena pressure is directed to the conductor it will urge apart and thecircuit will be broken. In U.S. Pat. No. 6,396,010 such a breakingelectric circuit is disclosed. However, the circuit in U.S. Pat. No.6,396,010 has a very complex construction comprising precisionmanufactured metal sheets. Another solution is disclosed in EP 0234523,where a breaking circuit is formed by plastic balls and an inner metalconductor with contact sheets. Also this device a complex construction.

Another common sensor type is pneumatic/hydraulic contact rails using,for example, contact sheets in which compressed-air apparatus comprisinga hermetically closed tube, conventionally in-built in rubber or softplastic, I combination with a compressed-air sensor, which upon apredetermined pressure obtained when the tube is compressed, registersand triggers a safety operation, for example, stopping the doors. To useair as a sensor is associated with significant drawbacks due to the factthe air is inherently sensitive for temperature variations. Since thecontact rails is placed at doorposts they often are exposed for largetemperature variations at opening/closing of the doors, which has asignificant negative impact of the reliability of the rails. Devicesthat utilizes liquids is also used to a certain extent but since liquidsalso are influenced by temperature variations, these devices suffer fromthe same problem. Moreover, pneumatic/hydraulic devices are affected bymechanical damage. In U.S. Pat. No. 4,133,365 a device using pneumaticedge detecting of double doors is disclosed.

In other devices fibre optic that responds to pressure are used. Fibreoptic has a much higher durability against disturbances such astemperature differences, but is sensitive to mechanical damage, which iscommon at doorways.

Another type of sensors are so called non-contact sensors, for example,volume sensors, line-light sensors, and capacitive sensors. Volumesensors are mainly constituted of sensors for ultra light and infraredlight. In both cases there are significant difficulties in limiting anddirecting the target area so that false detection do not occurred. Invehicles, for example, busses and underground trains, where the body canbe curved and in which doors and bodies moves considerably during thetransportation, volume sensors are not practical applicable. The sameapplies to line sensors in which optical light rays are used, which raysare sensitive to movements of the point of attachment. In U.S. Pat. No.4,621,452 and PCT/SE87/00405 such sensor systems are described.Capacitive sensors solve many of the above mentioned problem but theycan only detect conductive objects. Such systems are described in, forexample, DE 3521004, U.S. Pat. Nos. 3,370,677 and 4,976,337.

All of the above described sensor systems are not construed to preventpeople and object from being pushed and/or squeezed between doors orbetween a door and a door post. Due to the design of the sensors therequirement of that all of the door edge should be sensing. This isespecially important at the lower part of the edge of the door where afoot or a hand may be stuck.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a capacitive squeezeprotecting device for ports and doors, and in particular for automaticdoors, which is able to simultaneously detect physical pressure ofconductive as well as non-conductive object and persons or conductiveobjects within a protection or measurement field generated by anantenna. By careful measurements using a capacitive detector thedistance to a foreign conductive object or person can be measured. Thecapacitive detector fulfils the requirements of EMC and is capable ofgenerating a balanced field that surrounds the antenna and that is notaffected by variations in moisture or temperature so as to detect smallcapacitive variations of the generated filled that surrounds theantenna. The compressive force applied on the squeeze protecting devicecan also be indicated accurately. This and other objects are achievedaccording to the present invention by a squeeze protecting device,system and method having the features defined in the independent claims.Preferred embodiments are defined in the dependent claims.

A squeeze protecting device according to a first aspect of the inventioncomprises a housing and an antenna unit connected to a detectingcircuit, which circuit is arranged to detect capacitive variations, viasaid antenna unit, in an electric or electromagnetic field around saidantenna unit. Furthermore, the detecting unit comprises means connectedto said antenna unit arranged to detect a variation of the pressure atsaid antenna unit caused by a compressive force applied at said housing,wherein the presence of conductive as well non-conductive objects insaid protection field can be detected.

A squeeze protecting device according to a second aspect of the presentinvention comprises a housing and an antenna unit connected to adetecting circuit, which circuit is arranged to detect capacitivevariations, via said antenna unit, in an electric or electromagneticfield around said antenna unit. The antenna unit comprises a pluralityof conductive elements connected to said detecting circuit and saiddetecting circuit comprises means connected to said antenna unitarranged to detect a compressive force applied to said housing as avariation of the distance between a first and a second conductiveelement of the antenna unit, wherein the presence of conductive as wellas non-conductive object in said protection field can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS

Above-mentioned and other features and advantages of the presentinvention will be apparent from the following detailed description ofpreferred embodiments, merely exemplifying, in conjunction with theattached drawing, wherein:

FIG. 1 is a circuit diagram according to first embodiment having ananalogous capacitive detecting circuit;

FIG. 2 is a circuit diagram according to second embodiment having acapacitive detector partly based on a microprocessor architecture;

FIG. 3 a is front view of a door provided with contact rails accordingto the present invention;

FIG. 3 b is a top view of a door provided with contact rails accordingto the present invention;

FIG. 4 shows a perspective view a first embodiment of a contact railprovided with a squeeze protecting device according to the presentinvention;

FIG. 5 shows the connection of the contact rail in FIG. 4 to a detectingcircuit according to FIG. 1, 2, or 8;

FIGS. 6 a-c show in cross-section how the measurement field generated atthe rail shown in FIGS. 4 and 5 can be directed in different directions;

FIG. 7 a shows in cross section a second embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 7 b shows in cross section a third embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 8 shows a third embodiment of a circuit diagram having an analogouscapacitive detecting circuit;

FIG. 9 a shows a fourth embodiment of a contact rail with squeezeprotection according to the present invention;

FIG. 9 b shows in cross section a fifth embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 9 c shows in cross section a sixth embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 9 d shows in cross section a seventh embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 9 e shows in cross section a eighth embodiment of a contact railprovided with squeeze protection according to the present invention;

FIG. 9 f shows in cross section a ninth embodiment of a contact railprovided with squeeze protection according to the present invention;

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference first to FIG. 1, an electric circuit 2 and an antenna 4constituting a preferred embodiment of a capacitive detecting couplingwhich may well be used in the present invention.

The electronic circuit 2 has a square wave generator 6 having an outputconnected to ground and a second output connected to an adjustableresistor 8. The second output is also connected to the negative input ofan operational amplifier 14. The other end of the adjustable resistor isconnected to a low-pass filter comprising a resistor 10 and a capacitor12 and to the positive input of operational amplifier 14. Capacitor 12included in low-pass filer is connected to ground and resistor 10 isconnected to antenna 4. The output of operational amplifier 14 is, via ahigh-pass filer 16 and a peak value rectifier 18, connected to thepositive input of a operational amplifier used as a voltage follower 20.The output of voltage follower 20 is used as a feed-back for thenegative output thereof. The output of voltage follower 20 is alsoconnected to the negative input of a comparator 22, the positive inputof a comparator 24 and via a resistor 26 and a summing node 28 to thepositive input of a voltage follower 30. The positive input ofcomparator 22 is fed by a voltage reference from a voltage dividercomprising two resistors 32 and 34. Resistor 32 is connected to apositive feed voltage and resistor 34 is connected to ground. The outputof comparator 22 is, via resistor 36 and summing node 28, connected tothe positive output of voltage follower 30. Summing node 28 is connectedto ground via capacitor 38. The output of voltage follower 30 is, via aresistor 40 used as a feed-back, connected to the negative outputthereof. This output is also, via resistor 40, used as a input to squarewave generator 6, thereby closing the loop. The direct output of voltagefollower 30 is via a potential meter 42 used as a negative input tocomparator 24 the output of comparator 24 is connected to ground via aresistor 44.

Thus, the physical construction of the capacitive detector has beendescribed and the description will now be concentrated on the functionof the different elements in the electronic circuit 2, which constitutesthe capacitive detector.

The configuration of the antenna 4 can be varied in a number ofdifferent ways depending on the application of the capacitive detector.

Square wave generator 6, whose output level is adjustable, generates asquare wave, 50-5000 Hz, which is applied to the antenna 4 via theadjustable resistor 8 and low-pass filter 10, 12. The applied squarewave generates an electric field at the antenna 4. The capacitive loadcaused by the surrounding construction of the antenna 4 is typicallyapproximately 50-500 pF.

The object of the adjustable resistor 8 is to adapt the square wave tothe conditions given by the specific environment in order to establish abalanced working point at the output of voltage follower 20.

This balanced working point is used as a reference in comparisons withrapid variations of the electric field. Initially, the adjustableresistor 8 is set so that the working point at the output of the voltagefollower 20 is equal to the reference voltage applied to the comparator20 via the voltage divider 32, 34. The adjustable resistor 8 can also berealized as a digitally controlled resistor if the capacitive detectoris realized in microprocessor architecture, which will be described inmore detail below.

The low-pass filter 10, 12 is used to stabilize and balance the electricfield generated of the antenna 4 and to prevent RF-signals from beingfed into the electric circuit 2, which otherwise may cause disturbances.Optionally, an inductor (not shown) can be connected in series withresistor 10, if that is necessary to stabilize and balance the electricfield at the antenna 4.

Operational amplifier 14, which at its negative input is fed with thesquare wave generated by square wave generator 6 and at its positiveinput is fed with the square wave affected by the capacitive load of theantenna 4, amplifies the difference thereof.

Operational amplifier 14 operates with an amplification of approximately300,000, i.e. with an open loop amplification. This is necessary so asto detect small variations in the generated capacitive field.Operational amplifier 14 has among its parameters “Common Voltage ModeRange”, CVMR. CVMR defines +/−working range which the input signal mustbe within in order to be amplified linearly. If the input signal isoutside CVMR, the operational amplifier 14 will be blocked and theoutput will either be high of low. By balancing the variable high levelof the generated square wave so that it exactly is kept within CVMR,unnecessary parts of the signal is blocked and, thus, only a small partof the square wave is amplified. This part has the highest sensibilitywith respect to capacitive influence. The capacitive influence on thesignal of the antenna 4 has the characteristic charging and dischargingcurve. The differential measurement performed by operational amplifier14 measures the difference between the uninfluenced square wave and thesquare wave influenced by the antenna capacitively. Since the values ofthe components of the electric circuit is very important so as tobalance the operational amplifier 14 in an accurate way, they are listedin a separate component list following after the description.

High-pass filter 16 is used to filter DC components. This is performedso as to eliminate the effect of temperature and moisture variations,which may influence the accuracy of the capacitive measurement.

Voltage follower 20 is used to separate the detecting part of thecircuits 2 from subsequent circuits. This is performed so as to limitthe influence of the subsequent circuits on the top value rectifier 18.

Voltage follower 30 is also used to limit the influence of subsequentcircuits thereof on the capacitor 38 and resistors 26 and 36.

Comparator 22 is used to stabilize and balance square wave generator 6.Voltage divider 32, 34 feeds comparator 22 with the reference voltage,which is to be compared with the output of voltage follower 20. Theoutput of comparator 22 generates an inverted polarity compared withvariations of the output of voltage follower 20. Capacitor 38 isarranged to prevent oscillation at comparator 22, i.e. the regulationwill be dampened with a time constant R*C, where C is the value ofcapacitor 38 and R the value of resistor 36.

Comparator 24 is used to detect variations of the generated electricfield at the antenna 4. These capacitive variations have a typicalvalues of 2-10 pF when a human body enters the electric field. Thepositive input of comparator 24 is the output of voltage follower 20.During normal circumstances, i.e. when no variations of the electricfield occur, this positive input corresponds to the reference voltage.The negative input of comparator 24 is fed from the output of voltagefollower 30 via potential meter 42, which also corresponds to thereference voltage. Potential meter 42 is used to set the level at whichthe capacitive detector is to indicate that a change in the electricfield has occurred, for example, when a person is closer the antenna 4than a predetermined distance.

The described embodiment is constructed of analogous circuits, but ofcourse it can also be realized in a microprocessor based architecture orother architectures by the man skilled in the art without departing fromthe scope of the invention.

FIG. 2 shows a second embodiment of the capacitive detector, whichpartly uses a microprocessor 46 based architecture, suitable for use inthe present invention. It operates in a corresponding manner as thecapacitive detector described with reference to FIG. 1 and willtherefore not be described again. An advantage with this secondembodiment is that the output indicating a change in the electric fieldat the antenna 4 can be divided in several different levels.

With reference now to FIGS. 3 a and 3 b, the principle use of theinvention in will be shown. In FIG. 3 a a front view of an automaticdoor 50 having a contact rail 52 according to the invention arrangedalong the impact edge 54. The protection fields generated from the railsare indicated with the shaded field 56. In FIG. 3 b a top view of anautomatic door 50 having contact rail 52 arranged along the impact edge54 and a contact rail arranged along the door blade. The protectionfields generated from the rails are indicated with the shaded field 56.It should be noted that both FIG. 3 a and FIG. 3 b are schematic viewsand not according to scale.

In FIGS. 4 and 5, a first embodiment of the present invention is shown.This embodiment is a non-touch contact rail in the form of anon-conductive rubber profile provided with conductive conductors whichconstituting antennas for capacitive measurements. Of course, othermaterial than conductive rubber may be used for the antennas.

The contact rail 60 includes an antenna unit 62, which in thisembodiment comprises uniform antenna elements 62 a, 62 b, 62 c, and 62d. The antenna elements is separated with a first isolating material 76,for example, foam. The antenna elements 62 a, 62 b, 62 c, and 62 d isarranged rectangular in pairs via a respective relay 64 a, 64 b, 64 c,and 64 d connected to a detecting circuit 66, see FIG. 5. For example, adetecting circuit of the type shown in FIG. 1 or FIG. 2 can be used.This construction makes it possible to select which of the antennaelements who will function as signal /measurement antenna by switchingon the desired element by means of relays 64 a, 64 b, 64 c, and 64 d.Then, the other elements will function as screening elements or,alternatively, as grounding elements to amplify the variation at themeasurement antenna.

Furthermore, the rail comprises a housing 70 of deformable rubber orplastic. The housing is filled with a second isolating material 78. Toeliminate the risk that water running on the housing forms bridges toground, flanges 72 are arranged in the housing in order to breakpossible water bridges. A conductive conductor 74 connected to theoscillator may preferably be arranged in the contact rail to stabilizethe signal measurement environment. Due to the fact that the housing isentirely filled with isolating material the problem with condensationwithin the housing is avoided. Moreover, a fastening device 77 isarranged at the lower end of the rail for mounting at, for example, adoor.

By selectively switching on or off one or more antennas is it possibleto direct the interrogation or measurement field, see FIGS. 6 a-6 c. InFIGS. 6 a-6 c, a cross-section views of the rail according to the firstembodiment are shown. In FIG. 6 a, the element 62 a is switched on andfunctions as a measurement antenna whereas the remaining elements thatare switched off function as screening elements. The measurement field68 will, in this case, be directed straight forward in relation to thelocation of the rail at the edge of the door or, in other words, with aangle of 90 degrees to the surface of the active element. In FIG. 6 b,both element 62 a and element 62 b are switched on, whereas only element62 c and element 62 d are switched off, and accordingly function asscreening elements. Thereby, the measurement or protection field 68 willbe directed obliquely forward in relation to the location of the rail atthe door edge or with an angle of 45 degrees to the surface of element62 a and 62 b. In FIG. 6 c is only element 62 b switched on andfunctions as a measurement antenna whereas the others are inactive.Thereby, it is possible to direct the measurement field obliquely inrelation to the location of the rail at the edge of the door or with anangle of 90 to the surface of the active element 62 b.

Thus, according to the embodiment of the present invention shown inFIGS. 4, 5 and 6 a-6 c comprising four conductive conductors or antennaelements 62 a, 62 b, 62 c, and 62 d, the conductors can function eitheras measurement antennas or as screen antennas, which makes it possibleto direct the protection or measurement field in a desired direction. Bymeans of the detector shown in FIG. 1 or 2 is possible to detect smallcapacitive variations in the generated field that surrounds the antenna(antennas), for example, if a person is moving in the area of the field.

Respective conductor pair, in this case 62 a and 62 c, 62 b and 62 d,respectively, form a capacitor in which the conductors function ascapacitor plates. The dimensions of the conductors, the distance betweenthe conductors of respective pair, the material of the conductors andthe isolating material 76 determines the capacitance in F. Thecapacitance is changed when the distance between the conductors ischanged, given fixed dimensions and materials. Changes of the distanceare caused by a compressive of the rail by a compressive force, forexample, when a person or an object comes into contact with the rail.

The rail according to the present invention is able to accordinglydetect physical pressure from conductive as well as non-conductiveobject. Moreover, is able to detect persons or conductive objects withinthe measurement or protection area.

Of course, the construction of the conductors, the material, and thenumber of conductors can be varied. Consequently, in FIG. 7 a, anotherembodiment of the rail in accordance with the present invention, inwhich two antenna units are used, is shown. The rail comprises a housing80, which may, for example, consist of non-conductive rubber, filledwith an isolating material 82. To eliminate the risk that water runningon the housing forms bridges to ground, flanges 84 are arranged in thehousing in order to break possible water bridges. Furthermore, anmeasurement antenna 86 arranged to, when it is switched on, generate ameasurement field 88 for detecting conductive objects or persons. Theantenna 86 is connected to a detecting circuit (e.g. of such type shownin FIG. 1, 2, or 8). A screen antenna 90 is arranged in parallel withthe measurement antenna. According to an alternative embodiment, thescreen antenna is replaced by a ground plane. If a screen antenna isused is it possible to perform measurements at longer distances sincethe coupling to ground is decreased.

The conductor pair, i.e. the measurement antenna 86 and the screenantenna 90, form a capacitor where the conductors function as capacitorplates. The dimensions of the conductors, the distance between theconductors of respective pair, the material of the conductors and theisolating material 82 determines the capacitance in F. The capacitanceis changed when the distance between the conductors is changed, givenfixed dimensions and materials. Changes of the distance are caused by acompressive of the rail by a compressive force, for example, when aperson or an object comes into contact with the rail.

The smaller the distance between the conductors, the higher thesensitivity to compressive forces will become. By arranging notches atthe housing, a more effective detecting of compressive forces areachieved, in a direction from the side as well as from straight ahead.

In FIG. 7 b, a further embodiment having internal distance measurementand contacting capability, which enables a redundant system it is shown.The rail comprises a housing 80 of a conductive material, for example, aconductive rubber. In this embodiment, the housing 80 also functions asa ground plane. Furthermore, the rail comprises an antenna element 86having circular cross section and an isolating material 82. Due to thecircular construction of the antenna, a impact angle of 180 degrees ormore is obtained. Since the housing is conductive, no externalmeasurement field will be generated.

With reference now to FIG. 8, an additional detecting circuit 100, thatcan be used for detecting pressure against an antenna element as well ascapacitive variations in a measurement field generated by an antennaelement, is shown schematically. The circuit 100 may, for example, beconnected to the rail shown in FIG. 7. The circuit comprises anoscillator 104 connected to a resistive network 114, a band-pass filter106, a trigger circuit 108, a relay 110 and a detecting unit 112 fordetecting a pressure against a measurement antenna 102 as a change ofthe distance between the measurement antenna 102 and a ground plane 116(or a screen antenna). It should be noted that the circuit shown in FIG.1 or 2 also can be used.

By switching on a screen antenna to a non-processed oscillator signalfrom the oscillator 104 in the resistive network 114, in combinationwith the measurement antenna 102, the following functions can beachieved.

-   -   1. The measurement field can be divided in action levels. For        example, a first level may entail that the door slows down to        half the original speed and a second level may trigger an        emergency stop of the door or a reverse movement of the door.    -   2. The protection field may regulate the speed of the door so        that it is adjusted in accordance with the walking speed of the        pedestrian.    -   3. Further functions can be obtained by utilizing a physical        compressive between the different conductors, which leads to        significant results. For example, a contacting between the        conductor of the measurement signal and ground may give rise to        a positive indication whereas a contacting between the conductor        of the non-processed oscillator signal and the measurement        signal, respectively, may give rise to negative indication. In        other cases the contacting between the conductors of ground and        the non-processed oscillator signal, respectively, may be used.

With reference to FIGS. 9 a-9 f, further embodiments of the rail inaccordance with the present invention are shown in cross section. I allof FIGS. 9 a-9 f, the same element is indicated with the same referencenumeral according to the following table.

TABLE 1 Element Reference numeral Measurement antenna 120 Screen antenna122 Ground plane 124 Isolating material, e.g. foam 126 Housing 128

The rail according to FIG. 9 a has a housing 128 of a non-conductingmaterial, for example, non-conductive rubber. Two screen antennas 122 isarranged within the housing 128 on either side of a measurement antenna120. The rail shown in FIG. 9 a detects both conductive persons andobject in the measurement area as well as compressive forces. Thecompressive force can be measured as the degree of compressive.

Also the rail shown in FIG. 9 b has a housing 128 of a non-conductingmaterial, for example, non-conductive rubber. A screen antenna 122, ameasurement antenna 120 and a ground plane 124 are arranged in thehousing. The space between the screen antenna 122 and the measurementantenna 120 is filled with a isolating material 126, for example foam.The rail shown in FIG. 9 b detects both conductive persons and object inthe measurement area as well as compressive forces. The compressiveforce can be measured as the degree of compressive.

The rail shown in FIG. 9 c has a housing 128 of a non-conductingmaterial, for example, non-conductive rubber. A measurement antenna 120and a ground plane 124 are arranged in the housing. The space betweenthe ground plane 124 and the measurement antenna 120 is filled with aisolating material 126, for example foam. Since the rail according toFIG. 9 c is completely filled, it is insensitive to condensation water.Moreover, it has a high durability for torsional forces. The rail shownin FIG. 9 d has a housing 128 of a conducting material, which functionsas a ground plane in conjunction with a ground plane 124 arranged insidethe housing 128. Furthermore, a measurement antenna 120 is arranged onan element 126 of isolating material, for example, foam. The rail shownin FIG. 9 d detects both conductive persons and object in themeasurement area as well as compressive forces. The compressive forcecan be measured as the degree of compressive.

The rail shown in FIG. 9 e has a housing 128, of which the upper part inthe figure functions as a screen antenna 122 and the lower partfunctions as a ground plane 124. Furthermore, a measurement antenna 120is arranged on an element 126 of isolating material, for example, foam.The rail shown in FIG. 9 e detects both conductive persons and object inthe measurement area as well as compressive forces. The compressiveforce can be measured as the degree of compressive.

The rail shown in FIG. 9 f has a housing 128 of conductive material,which functions as a ground plane 124. Furthermore, a measurementantenna 120 and a screen antenna 122 are arranged on an element 126 ofisolating material, for example, foam. The rail shown in FIG. 9 fdetects both conductive persons and object in the measurement area aswell as compressive forces. The compressive force can be measured as thedegree of compressive.

All of these rails can be used in the detecting circuits shown in FIGS.1, 2, and 8.

In operation, the field generated at the rail will react when the doorapproaches the door post (ground plane), at mounting on double doors, itwill react on the other door, since it is detected in the same way as aforeign object or a foreign person. To eliminate this, a synchronizationmay be performed by means of positioning sensor in the drive unit of thedoor, which at a given position will send a control instruction to thedetecting circuit to perform the measurement at a smaller distance fromthe rail. Due to the fact that the speed of the door is decreasedsimultaneously, the stopping distance will be shorter for which reasonthe smaller field can adjusted to contact with the rubber edge. Thus,the extension of the measurement field is determined by the movement andspeed of the door. Another solution is to always send a control signalto drive unit of the door, which instruct it to decrease the speed ofthe door at the end of the shutting movement and to simultaneouslychanging to a field having a smaller extension, change the direction ofthe measurement field (see FIGS. 6 a-6 c), or to block the field. Afurther method to prevent an undesired reaction at the door post is tomask the door post by either divide the measurement antenna and mountone part above the door post or to mount a conductor for the oscillatorsignal at the door post so that an appropriate part of the door iscovered by an identical signal. Yet another method to prevent anundesired reaction at the door post is to arrange a separate non-contactcontact rail with associated electronic (e.g. the detecting circuit, seeFIG. 1, 2, or 8) at the door post and to synchronize the oscillators sothat the signals are identical.

Even if the, at the present, preferred embodiments of the invention hasbeen described, is it obvious for the man skilled within the art fromthe description that variations or adaptations of the presentembodiments can be implemented without departing from the principles ofthe invention.

Thus, the intention that the invention is not to regarded as limited toonly the structural or functional element described in the embodiments,but to the attached claims.

List of components Reference numeral Component (value) 8 0-10 kΩ 10 3,3kΩ 12 47 pF 14 ca 3160 E 20 TL 074 22 LM 339 24 LM 339 26 L MΩ 30 TL 07433 2,84 V 36 1 MΩ 38 100 μF 40 200 Ω

The invention claimed is:
 1. Squeeze protecting device arranged to detect the presence of an object in a protection area comprising a housing and an antenna unit connected to a detecting circuit, which circuit is arranged to, via said antenna unit, detect capacitive variations in an electric- or electro-magnetic field at said antenna unit, characterised in that said detecting circuit comprises a signal generator that provides a signal to the antenna unit that generates the electric or electro-magnetic field at the antenna unit; balancing means for maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; filter means for preventing the detecting circuit from being affected by variations in temperature and moisture; and detecting means for detecting small variations in the generated electric or electromagnetic field at the antenna unit and/or a variation of pressure at said antenna unit caused by a compressive force applied to said housing, wherein the presence of conductive as well as non-conductive objects in said protection area can be detected.
 2. Squeeze protecting device according to claim 1, characterised by that said antenna unit comprises a plurality of conductive elements connected to said detecting circuit.
 3. Squeeze protecting device according to claim 1, wherein the detecting circuit detects the compressive force as a variation of the capacitance between a first conductive element and a second element of the antenna unit.
 4. Squeeze protecting device arranged to detect the presence of an object in a protection field comprising a housing and an antenna unit connected to a detecting circuit, which circuit is arranged to, via said antenna unit, detect capacitive variations in an electric- or electro-magnetic field at said antenna unit, characterised in that said antenna unit comprises a plurality of conductive elements connected to said detecting circuit, wherein the detection circuit comprises: a signal generator that provides a signal to the antenna unit that generates the electric or electro-magnetic field at the antenna unit; balancing means for maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; filter means for preventing the detecting circuit from being affected by variations in temperature and moisture; and detecting means for detecting small variations in the generated electric or electromagnetic field at the antenna unit and/or detecting a compressive force applied at said housing as a variation of the distance between a first conductive element and a second conductive element of the plurality of conductive elements, wherein the presence of conductive as well as non-conductive objects in said protection field can be detected.
 5. Squeeze protecting device according to claim 4, characterised in that each of said conductive elements of said antenna unit is connected to said detecting circuit via a relay, wherein said electric or electromagnetic field can be directed in a desired direction by switching on or off, respectively, suitable conductive elements of the antenna unit.
 6. Squeeze protecting device according to claim 1 or 4, wherein the detecting circuit detects the compressive force as a variation of the capacitance at said antenna unit.
 7. Squeeze protecting device according to claim l or 4, characterised in that said housing comprises a first isolating material and that said antenna unit comprises a second isolating material.
 8. Squeeze protecting device according to claim 1 or 4, characterised in that said antenna unit has a circular cross section.
 9. Squeeze protecting device according to claim 1 or 4, characterised in that masking means is arranged at a grounded object located adjacent to said squeeze protecting device, wherein a detection of said grounded object as a conductive object is avoided.
 10. Squeeze protecting device according to claim 9, characterised in that said masking means comprises a conductor connected to said detecting circuit arranged on the grounded object located adjacent to said squeeze protecting device, wherein the detection of said grounded object as the conductive object is avoided.
 11. Squeeze protecting device according to claim 9, characterised in that said masking means comprises a conductive element connected to said antenna unit mounted at the grounded object located adjacent to said squeeze protecting device, wherein the detection of said grounded object as the conductive object is avoided.
 12. A contact rail provided with the squeeze protecting device according to claim 1 or
 4. 13. Method for, at a squeeze protecting device arranged at a door, detecting the presence of an object in a protection field, which squeeze protecting device comprises a housing and an antenna unit connected to a detecting circuit, comprising the step of, via said antenna unit, detecting capacitive variations in an electric or electromagnetic field at said antenna unit, characterised by the steps of: detecting a variation of the pressure at said antenna unit caused by a compressive force applied to said housing, generating an electric or electromagnetic field at the antenna unit; maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; preventing the detecting circuit from being affected by variations in temperature and moisture; detecting small variations in the generated electric or electromagnetic field at the antenna unit; and indicating that a variation in the electric or electromagnetic field at the antenna unit has occurred, wherein the presence of conductive as well as non-conductive objects in said protection field can be detected.
 14. Method according to claim 13, characterised by the step of detecting the compressive force applied to said housing as a variation of the distance between a first and a second conductive element of said antenna unit.
 15. Method for, at a squeeze protecting device arranged at a door, detecting the presence of an object in a protection field, which squeeze protecting device comprises a housing and an antenna unit connected to a detecting circuit, comprising the step of, via said antenna unit, detecting capacitive variations in an electric or electromagnetic field at said antenna unit, characterised by the steps of: detecting a variation of the distance between a first and a second conductive element of said antenna unit; generating an electric or electromagnetic field at the antenna unit; maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; preventing the detecting circuit from being affected by variations in temperature and moisture; detecting small variations in the generated electric or electromagnetic field at the antenna unit; and indicating that a variation in the electric or electromagnetic field at the antenna unit has occurred, wherein the presence of conductive as well as non-conductive objects in said protection field can be detected.
 16. Method according to claim 13 or 15, characterised by the step of directing said electric or electromagnetic field in a desired direction by switching on or off, respectively, suitable conductive elements.
 17. Method according to claim 13 or 15, characterised by the step of masking a grounded object located adjacent to said squeeze protecting device, wherein a detection of said grounded object as a conductive object is avoided.
 18. Method according to claim 17, characterised in that said step of masking comprises the step of arranging a conductor connected to said detecting circuit on the grounded object located adjacent to said squeeze protecting device, wherein the detection of said grounded object as the conductive object is avoided.
 19. Method according to claim 17, characterised in that said step of masking comprises the step of mounting a conductive element connected to said antenna unit at the grounded object located adjacent to said squeeze protecting device, wherein the detection of said grounded object as the conductive object is avoided.
 20. System for detecting the presence of an object in a protection field, comprising a contact rail for mounting at an automatic door and a detecting circuit connected to an antenna unit arranged in said rail, which circuit is arranged to, via said antenna unit, detect capacitive variations in an electric- or electro-magnetic field at said antenna unit, characterised in that said detecting circuit comprises: a signal generator that provides a signal to the antenna unit that generates the electric or electro-magnetic field at the antenna unit; balancing means for maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; filter means for preventing the detecting circuit from being affected by variations in temperature and moisture; and detecting means for detecting small variations in the generated electric or electromagnetic field at the antenna unit and/or a variation of pressure at said antenna unit caused by a compressive force against said rail, wherein the presence of conductive as well as non-conductive objects in said protection field can be detected.
 21. System for detecting the presence of an object in a protection field comprising a contact rail for mounting at an automatic door and a detecting circuit connected to an antenna unit arranged in said rail, which circuit is arranged to, via said antenna unit, detect capacitive variations in an electric- or electro-magnetic field at said antenna unit, characterised in that said antenna unit comprises a plurality of conductive elements connected to said detecting circuit and that said detecting circuit comprises: a signal generator that provides a signal to the antenna unit that generates the electric or electro-magnetic field at the antenna unit; balancing means for maintaining the generated electric or electromagnetic field at the antenna unit in a balanced condition; filter means for preventing the detecting circuit from being affected by variations in temperature and moisture; and detecting means for detecting small variations in the generated electric or electromagnetic field at the antenna unit and/or detecting a compressive force applied at said rail as a variation of the distance between a first conductive element and a second conductive element of the plurality of conductive elements, wherein the presence of conductive as well as non-conductive objects in said protection field can be detected.
 22. System for detecting the presence of an object in a protection field according to claim 20 or 21, comprising another contact rail that is mounted on a grounded object located adjacent to said automatic door and that includes another detecting means, wherein the detecting means and said another detecting means are synchronized in order to provide identical signals such that a detection of said grounded object as a conductive object is avoided. 